Your body weight will fluctuate from day to day due to changes in your body’s fluid makeup. The human body is roughly 70% water. This percentage can be affected by changes in hormone levels, dietary factors such as salt and carbohydrate consumption, and even exercise. Weight changes over several weeks are more likely to reflect changes in levels of fat and muscle rather than fluid. Because the scale can’t distinguish between weight changes due to water, fat or muscle you shouldn’t allow every fluctuation in weight to rule your life.